1. Field of the Invention
The present invention is directed to biopolymer photonic crystals and methods for manufacturing such photonic crystals.
2. Description of Related Art
The field of optics is well established. Some subfields of optics include diffractive optics, micro-optics, photonics, and guided wave optics. Various optical devices have been fabricated in these and other subfields of optics for research and commercial application. For example, common optical devices include diffraction gratings, photonic crystals, optofluidic devices, waveguides, and the like.
Photonic crystals are periodic dielectric or metallo-dielectric structures that define allowed and forbidden electronic energy bands. In this fashion, photonic crystals are designed to affect the propagation of electromagnetic (EM) waves in the same manner in which the periodic potential in a semiconductor crystal affects electron motion.
Photonic crystals include periodically repeating internal regions of high and low dielectric constants. Photons propagate through the structure based upon the wavelength of the photons. Photons with wavelengths of light that are allowed to propagate through the structure are called “modes”. Photons with wavelengths of light that are not allowed to propagate are called “photonic band gaps”. The structure of the photonic crystals define allowed and forbidden electronic energy bands. The photonic band gap is characterized by the absence of propagating EM modes inside the structures in a range of wavelengths and may be either a full photonic band gap or a partial photonic band gap, and gives rise to distinct optical phenomena such as inhibition or enhancement of spontaneous emission, spectral selectivity of light, or spatial selectivity of light. Such structures can be used for high-reflecting omni-directional mirrors and low-loss waveguides. Photonic crystals are attractive optical devices for controlling and manipulating the flow of light. Photonic crystals are also of interest for fundamental and applied research and are being developed for commercial applications. Two-dimensional periodic photonic crystals are being used to develop integrated-device applications.
Advances in micro-technology and nanotechnology have led to the miniaturization of a number of devices. Applied scientists and researchers continue to attempt to engineer control matter on the atomic and molecular scale and to build devices in that size range. These scientists drawing from applied physics, materials science, interface and colloid science, device physics, chemistry, and engineering disciplines to bring existing technology to the nanoscale.
Lithographic techniques serve to facilitate development of nanoscale devices by selectively removing portions of thin films or substrates. Scanning probe lithography incorporates a microscopic stylus that is mechanically moved across a surface to form new patterns on the film. The new patterns are formed by mechanically deforming the surface of the film using nanoimprint lithography or by transferring a chemical to the surface of the film.
Dip Pen Nanolithography® (DPN) is a scanning probe lithography technique that may use an atomic force microscope tip to transfer molecules to the film surface using a solvent meniscus. This technique allows surface patterning on scales of under 100 nanometers. DPN is the nanotechnology analog of a quill pen, where the tip of an atomic force microscope cantilever acts as a “pen,” which is coated with a chemical compound or a mixture acting as an “ink,” and put in contact with a substrate, the “paper.”
DPN enables direct deposition of nanoscale materials onto a substrate in a flexible manner. The vehicle for deposition can include pyramidal scanning probe microscope tips, hollow tips, and even tips on thermally actuated cantilevers.
Photonic crystals and other optical devices are fabricated using various methods, depending on the application and optical characteristics desired. However, these optical devices, and the fabrication methods employed in their manufacture, generally involve significant use of non-biodegradable materials. For example, glass, fused silica, or plastic are commonly used in optical devices. Such materials are not biodegradable, and remain in the environment for extended period of time after the optical devices are removed from service and discarded. Of course, some of the materials can be recycled and reused. However, recycling also requires expenditure of natural resources, and adds to the environmental costs associated with such materials.
Therefore, there exists an unfulfilled need for optical devices such as photonic crystals that minimize the negative impact to the environment. In addition, there exists an unfulfilled need for photonic crystals that provide additional functional features that are not provided by conventional photonic crystals.